Conventionally, retroreflective materials that retroreflect incident light are widely used for indications such as traffic signs, or for identification of marine accident equipment, and particularly for improving visibility at nighttime. From the viewpoint of ensuring the safety of people who work at night, such retroreflective materials are also widely used as safety clothing for policemen, firefighters, workers involved in civil engineering and construction, and the like, in safety clothes, safety vests, sashes, arm bands, life vests, and the like. Furthermore, in recent years, along with a growing consciousness of the safety of life, or the diversification of decorativeness, such retroreflective materials are also used in apparel such as windbreakers, sweat suits, T-shirts, sports shoes, and swimming suits for preventing traffic accidents at nighttime, or used in bags, suitcases, and the like for decorative purposes.
When a retroreflective material has a printed pattern such as text, signs, or graphics, the printed pattern is visible at daytime, and retroreflected light is visible by light impinging on the retroreflective material at nighttime. By thus making the retroreflective material visible differently at daytime and nighttime, characteristics of the retroreflective material such as distinctiveness and design can be improved. Thus, retroreflective materials with printed patterns have been developed.
For example, Patent Literature 1 proposes providing a retroreflective material with a pattern by dyeing or applying a print with a graphic pattern to a fiber fabric serving as a support for the retroreflective material. Although the method disclosed in Patent Literature 1 is suitable for applications intended for mass consumption or applications with simple patterns, it is not practical in terms of cost, for applications for use in small lots, and requiring complicated patterns.
Patent Literature 2 discloses a method in which a surface of a retroreflective sheet is coated with a resin coating such as vinyl chloride, and then a desired pattern is formed on the resin coating surface by silk-screen printing using an ink of the same type as that of the coating resin. The retroreflective sheet disclosed in Patent Literature 2, however, is of a so-called encapsulated type in which there is a space on the surface of transparent microspheres (surface positioned opposite to the reflective layer), and the space is covered with a transparent plastic film. This retroreflective sheet has a possibility that the resin coating may be readily broken by a physical impact, and also has the drawback of being poor in wash resistance and handleability. Additionally, with regard to the retroreflective sheet disclosed in Patent Literature 2, the type of the resin used for the resin coating on which a pattern is printed has not been contemplated.
Patent Literature 3 discloses a retroreflective article comprising a core sheet having a viewing surface wherein the core sheet includes retroreflective elements; and a topcoat disposed on the viewing surface; wherein the topcoat essentially consists of at least one dried and optionally cured water-borne acrylic polymer, and the topcoat has a predetermined elastic modulus. Patent Literature 3 also discloses that the topcoat can be provided with a pattern by laser printing, ink-jet printing, or thermal mass transfer printing. However, when the surface of a retroreflective material is coated with an acrylic polymer as disclosed in Patent Literature 3, the retroreflective material has the drawback of having a hard texture, which makes it uncomfortable to wear when it is attached to clothing, for example. Such a retroreflective material with a hard texture also has the drawback of having poor wash resistance, which causes the external color and retroreflective performance to change after washing.
Patent Literature 4 discloses an ink receptive layer comprising a base polymer comprising a) a urethane acrylic copolymer, b) a blend of a polyurethane polymer and an acrylic polymer with predetermined molecular weights, c) a blend of at least two polyurethane polymers, and/or mixtures thereof, wherein the ink receptive layer is substantially free of filler. This ink receptive layer has the property of allowing a non-aqueous ink-jetted image to be readily formed thereon. Patent Literature 4 also discloses retroreflective articles comprising the ink receptive layer. However, when a retroreflective material has such an ink receptive layer formed using an acrylic resin such as an acrylic polymer or a urethane acrylic copolymer, the retroreflective material has the drawback of having a hard texture and poor wash resistance. Patent Literature 4 also proposes providing an ink receptive layer comprising a blend of at least two polyurethane polymers. The wash resistance of a daytime color visible by ink-jet printing varies significantly depending on the types of monomers forming the polyurethane polymers. Patent Literature 4, however, fails to sufficiently contemplate the types of monomers forming the polyurethane polymers, for achieving good wash resistance of the daytime color.